The physiological stress for the user of safety suits is very high because the inside temperature and the humidity in the suit increase very rapidly during physical stress. The high humidity of the air, in particular, causes that the person can no longer sufficiently release his body heat, because the heat is released predominantly by sweating during high physical stress. The mission of rescue teams with safety suits is very limited in time due to this circumstance and the duration of the mission is therefore at most only 10 to 20 minutes. If a long distance is to be covered to the site of the mission, only little time and energy is left for the rescue mission proper and the individual retreat.
Humans are definitely able to perform physical activity over several hours even at ambient temperatures of 42° C. if the humidity of the air is relatively low, i.e., below 30% relative humidity. Even though the body temperature rises somewhat in the process, it does, however, remain at a stable level in this case. The same applies to the heart rate.
The body temperature rises continuously at a markedly reduced air temperature of 32° C. but very high relative humidity of 84% and the test subject will become exhausted very quickly. The circumstance that exhaustion is accelerated by the fact that a respirator is also present on the person's body besides the safety suit is to be taken into consideration in case of persons who use a safety suit.
A safety suit, in which air is fed in from the outside by means of a blower and released from the safety suit via a pressure relief valve is known from EP 1 494 760 B1. Even though a measurable cooling effect arises due to the rinsing with air, the moisture cannot be prevented from accumulating in the interior space of the suit and from condensing on the material of the safety suit. The condensate collects partially on the clothing, which is unpleasant for the user of the suit. In addition, the blower draws in ambient air, which may be contaminated and must be thoroughly filtered. The residual risk that contaminated air can enter the interior space of the safety suit is not accepted by the users.
Cooling with a liquid is also used to cool or regulate the temperature of persons. This is used in space suits, but also in safety chemical suits. However, this principle is limited in its action because it acts directly on the skin via the conductive cooling action. The skin temperature must be kept so cool that no sweating will develop, and it leads as a result to unphysiological or very unpleasant, cold skin temperatures. The cooling source proper is arranged outside the suit. The total cooling energy must be carried along in case of a mobile device, which leads to heavy weights of approx. 12-18 kg additionally and to a correspondingly large volume. Water ice storage units carried along have corresponding net weights of 3.23 kg for the ice plus the own weight of the housing at a hypothetical cooling energy of 1,080 kJoules, which corresponds to a cooling capacity of 800 W over 30 minutes. The handling of the water ice is complicated because the ice must first be prepared and finally removed from the cooling containers and charged into the cooling device. A safety suit with a cooling source appears, for example, from DE 28 46 139 C2.
A safety suit, in which the air in the interior space is circulated by means of a blower and both carbon dioxide and moisture are removed in the process is known from U.S. Pat. No. 3,174,300. The oxygen consumed is replaced. A chamber filled with a refrigerant is used to separate moisture, and the condensate formed is collected in a collection tank. Even though the temperature and the humidity can be readily set in the interior space in the prior-art safety suit, a refrigerant must be carried along and replaced after a certain time of use. The cooling energy available is greatly limited by the weight of the refrigerant carried along.